The invention relates generally to computer-based methods for deriving contour data for vessels with differential absorption utilizing x-ray densitometry, and more particularly to such computer-based methodologies that detect vessel contours by the application of a contour-finding algorithm on a shadow image and segmentation based on image intensities. A prime field of application for such computer-based methodologies is in small, in particular sub-millimeter blood vessels. However, such computer-based methodologies may also be used for other vessels that may have differential X-Ray attenuation or for implanted objects such as stents. Such finding of contours or borders is standard technology in medical diagnostics and related arts.
Prior art, in particular, S. Molloi et al, Quantification of Coronary Artery Lumen Volume by Digital Angiography, © 2001 to the American Heart Association, Reprints from symolloi@uci.edu, have described that contour detection methods based on local grayscale levels can result in different diameter estimations than methods that measure the total attenuation of radiation caused by the vessel for use as an estimation of the cross sectional area. For a normal round vessel the latter will then also produce an estimate for the diameter. The reference makes however no systematic use of this finding.
The present inventors have experienced that sometimes vessels are identified as being too large when contour detection is based on local intensities (for instance a minimum cost algorithm is used, as mentioned in Gronenschild, E, et al., 1994, A Second Generation System for Off-Line and On-Line Quantitative Coronary Angiography. Catheterization and Cardiovascular Diagnosis 33:61-75). Generally, these overestimations are caused by noise and blur in the X-ray image. Especially in smaller vessels with diameters less than about 1 mm the effect is noticeable.
Such apparent enlargement of a vessel may compromise the diagnostics of inter alia coronary stenosis or may influence the results of studies on the efficiency of new clinical treatments. Note that other vessel locations than coronary arteries will be influenced in the same way and can benefit correspondingly from improvements.